Many proposals have been made heretofore for both mechanical and electronic measuring instruments. In general, these prior proposals involve measuring instruments specially designed for a particular application or purpose although some have the capability of performing more than one type of operation. All are subject to various disadvantages and shortcomings avoided by the present invention including high cost, excessive bulk and weight and, in particular, inability to perform various drafting operations and measuring chores normally associated with or related to layout and drafting operations. Illustrative prior art measuring instrument devices are disclosed in the following U.S. Pat. Nos.: Mentzel 2,557,450; Murrah 2,867,908; Henson et al. 3,012,328; Pascoe et al. 3,166,844; Lowy, 3,172,208; Engelsman 2,498,959; Lineback 3,412,238; Paulson 3,601,585; Zeldler 3,688,410; Peddle 3,544,773; Boyce 3,654,449; Peddle 3,564,220; Welch et al. 3,683,159; Raser 3,696,397; Culver et al. 3,728,551; Fausel 3,758,949 and Colbourn 3,912,926.
No one of these prior patents discloses an instrument capable of performing numerous drafting operations such as penciling, inking, scratching; none is suitable for use as a protractor or angle measuring or graduating device. Only Peddle U.S. Pat. No. 3,564,220 discloses an electronic measuring instrument which can be utilized to measure irregular plots or configurations. Raser depends upon the use of a massive main frame mounted on a carriage which must be moved in a strictly straight path as a long draft arm used to propel the device is pivoted laterally of the path of travel as necessary for a pointer on that arm to follow an underlying irregular trace. The carriage and arm drive separate semipolar encoders the readings of which must be processed into a computer using trigonometric relationships to convert the readings rectangular or cartesion coordinates. Fausel's non-portable two dimensional digitizer apparatus is mounted on a large table top and includes a scribe the movement of which in any planar direction is transmitted to separate X and Y readout counters by an exposed cable and pulley system and lacking the features and capabilities of this invention. Pascoe et al. differs from Fausel principally by substituting electrical components for Fausel's cable and pulley system. Colbourn discloses only a specific type of opto-electronic incremental encoder for sensing precise increments of shaft rotation. There are electronic area measuring devices available commercially such as, for example, various planimeter instruments manufactured by the assignee of the present invention. However, these instruments are restricted to use as planimeters and mechanical integrators and are lacking in the versatility and wide variety of other uses served so efficiently and effectively by the present invention.